Japanese Patent Application Publication No. 2009-214786 discloses a conventional vehicle travel support device that supports travel by recognizing the lane marks on the left and right of the road. When the distance between the left and right lane marks increases as the road branches off, the vehicle travel support device in Japanese Patent Application Publication No. 2009-214786 supports the travel by using the lane mark, as a reference, that extends along the road on which the vehicle is planned to travel.
Here, at a right turn lane on a local road, an exit lane on a freeway, or the like, the lane width increases along the planned travel road. Specifically, at the entrance of a right turn lane or the entrance of an exit lane on a freeway, a solid line representing the boundary between the road and a shoulder, the centerline of the road, or the like shifts outward along the planned travel road, thereby increasing the lane width. Thus, when the lane width increases at the entrance of a right turn lane on a local road or the entrance of an exit lane on a freeway, the above conventional vehicle travel support device supports the travel based on the solid line shifting outward, so that the vehicle will be guided toward the right side if there is the right turn lane and toward the left side if there is the exit lane. For this reason, there has been a problem of being unable to control the host vehicle to travel at an appropriate position within its lane.